The tips of 15 radicles were cauterised with nitrate of silver, and they grew as well as those above described with greased tips.  After an interval of 24 h., 9 of them were not at all curved towards the bottom of the sieve; 2 were curved towards it at angles of 20o and 12o from their former vertical position, and 4 had come into close contact with it.  Thus the destruction of the tip for a length of about 1 mm. prevented the curvature of the greater number of these radicles to the adjoining damp surface.  Of 24 control specimens, 23 were bent to the sieve, and on a second occasion 15 out of 16 were similarly curved in a greater or less degree.  These control trials are included in those given in the foregoing paragraph.

Avena sativa.—­The tips of 13 radicles, which projected between 2 and 4 mm. from the bottom of the sieve, many of [page 184] them not quite perpendicularly downwards, were coated with the black grease for a length of from 1 to 1 ½ mm.  The sieves were inclined at 30o with the horizon.  The greater number of these radicles were examined after 22 h., and a few after 25 h., and within these intervals they had grown so quickly as to have nearly doubled their lengths.  With the ungreased radicles the chief seat of curvature is at a distance of not less than between 3.5 and 5.5 mm., and not more than between 7 and 10 mm. from the apex.  Out of the 13 radicles with greased tips, 4 had not moved at all towards the sieve; 6 were deflected towards it and from the perpendicular by angles varying between 10o and 35o; and 3 had come into close contact with it.  It appears, therefore, at first sight that greasing the tips of these radicles had checked but little their bending to the adjoining damp surface.  But the inspection of the sieves on two occasions produced a widely different impression on the mind; for it was impossible to behold the radicles with the black greased tips projecting from the bottom, and all those with ungreased tips, at least 40 to 50 in number, clinging closely to it, and feel any doubt that the greasing had produced a great effect.  On close examination only a single ungreased radicle could be found which had not become curved towards the sieve.  It is probable that if the tips had been protected by grease for a length of 2 mm. instead of from 1 to 1 ½ mm., they would not have been affected by the moist air and none would have become curved.

Triticum vulgare.—­Analogous trials were made on 8 radicles of the common wheat; and greasing their tips produced much less effect than in the case of the oats.  After 22 h., 5 of them had come into contact with the bottom of the sieve; 2 had moved towards it 10o and 15o, and one alone remained perpendicular.  Not one of the very numerous ungreased radicles failed to come into close contact with the sieve.  These trials were made on Nov. 28th, when the temperature was only 4.8o C. at 10 A.M.  We should hardly have thought this case worth notice, had it not been